Dr. Jill Tarter has spent 35 years searching for extraterrestrial life in the universe. She has a Ph.D. in astronomy from the University of California, Berkeley.

SETI Institute

As a child, astronomer Jill Tarter would walk along the beaches of western Florida with her father and look up at the stars.

"I assumed, at that time, that along some beach on some planet, there would be a small creature walking with its dad and they would see our sun in their sky, and they might wonder whether anyone was there," she tells Fresh Air's Dave Davies. "But I never thought about it professionally until graduate school."

In graduate school, Tarter worked on a project designed to search radio frequencies for clues about extraterrestrial life forms. The project, known as SERENDIP, was part of the Search for Extra-Terrestrial Intelligence (SETI) program based at the University of California, Berkeley.

Tarter got hooked — and has devoted her life to the search for extraterrestrial life. Over the course of her career at SETI, she's searched nearby star systems for signs of alien life and headed up efforts to create new telescopes to scan the skies for signals.

"We don't know how to identify intelligence over interstellar distances, so what we do instead is use technology for a proxy," she says. "And we say, 'Can we look or listen in any way that could detect technologies that someone else might be using and might be modifying their environment in ways that would be detectable over interstellar distances?' "

Her work at SETI has not gone unrecognized. Tarter has received awards from NASA, Time magazine and the American Association for the Advancement of Science. In addition, Carl Sagan's novel Contact was largely based on her work.

Tarter recently stepped down as the head of research at SETI to focus on fundraising efforts. But she says the search for intelligent life will continue.

"We've hardly begun to search," she says. "The space that we're looking through is nine-dimensional. If you build a mathematical model, the amount of searching that we've done in 50 years is equivalent to scooping one 8-ounce glass out of the Earth's ocean, looking and seeing if you caught a fish. No, no fish in that glass? Well, I don't think you're going to conclude that there are no fish in the ocean. You just haven't searched very well yet. That's where we are."

Interview Highlights

On how radio telescopes are used

"Pragmatically, to date, we're using radio telescopes to listen for signals that are generated either for their own purposes or they're beacons, intended to attract the attention of us on emerging, young technology in the galaxy. And at optical wavelengths, instead of looking for signals that occupy only narrow range of frequency, we look for signals that are broadband — flashes of light — that last for a billionth of a second or less. And we're constantly thinking about what's the next new technology that we might innovate which in turn could be a better way of looking for extraterrestrial technologies. We do reserve the right to get smarter and we certainly don't think we know all there is to know."

On the electromagnetic spectrum

"Radio astronomy, optical astronomy, gamma ray astronomy — they're all studying light. But light at different wavelengths — the shorter wavelengths, the higher frequencies. Those are the X-rays and the gamma rays and they speak and tell us about really energetic events in the cosmos — lots of explosions. The optical part of the spectrum — that light tells us about things that are 6,000 to 10,000 degrees in temperature. ... And the radio wavelengths — the longer wavelengths — there you study very cold matter. You study molecules and atoms and dust. So each part of the electromagnetic spectrum allows us to learn something different about the universe and about its physical properties. So radio wavelengths are just long, tired light."

On discoveries made while reviewing radio signals

"Early on in my career in France, I stayed awake for three days to prove a signal was a distant airport rather than something we were interested in because I thought my French colleague was going to call up Le Monde and tell them we found it. And another instance, I was at Green Bank, W.Va., and we had a second telescope in Georgia that helped us discriminate against our own technology. Unfortunately, this telescope got hit by lightning and we had three days to observe without it. And during that time, of course, we got a signal that was really interesting and we followed it for almost a whole day before we convinced ourselves that indeed, it was not coming from the star we had been tracking. It was a signal coming in from the sidelobes of the telescope. And this was a spacecraft that was orbiting the sun, and so was the planet Earth."

On our connection to the cosmos

"We are made out of stardust. The iron in the hemoglobin molecules in the blood in your right hand came from a star that blew up 8 billion years ago. The iron in your left hand came from another star. We are the laws of chemistry and physics as they have played out here on Earth and we are now learning that planets are as common as stars. Most stars, as it turns out now, will have planets."

On how finding a signal from an extraterrestrial being relates to Earth's future

"If we detect a signal, even if there's no information — even if it's just a cosmic dial tone — we learn that it's possible for us to have a future — a long future. And that's because we couldn't possibly be successful with SETI unless technologies, on average, survive for a long time so that they can be lined up not just in three-dimensional space — close enough for us to find them — but in the fourth dimension, in time — so that they're transmitting as we're emerging."

On an error in the movie Contact, which was based on her life

"It's just before the first kiss, so Jodie Foster is out on the balcony behind the control room and they're looking at the stars and the beautiful telescope and she's doing, 'Oh, look at all of those stars. If only one in a million of those stars had planets, and only one in a million of those planets had life, and if only one in a million of those lifeforms were transmitting, there would be millions of signals for us to detect.' The math is all wrong. It's really annoying. There are 100 billion stars in the Milky Way galaxy. And even if she was looking up and seeing them all, which she wasn't, she's multiplying 1011 * 10-18 and coming up with 106. That's wrong by 13 orders of magnitude. And the really sad story is that Carl Sagan died while this movie was being edited. And there was a memorial service for Carl in the spring. And [someone] wanted to show the assembled scientists and engineers a clip from the film. ... So [the kiss clip] is the clip that's shown, and you hear this gasp at the end from all the scientists and engineers who can obviously do the math and know it's wrong."

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

TERRY GROSS, HOST:

This is FRESH AIR. I'm Terry Gross. If we're ever contacted by beings from another planet, our guest, Jill Tarter, may be one of the first people to know. Tarter is an accomplished scientist who spent much of her career looking for signs of extraterrestrial life. Earlier this year, Tarter stepped down from her position as director of research for the SETI Institute. SETI - that's S-E-T-I - stands for Search for Extraterrestrial Intelligence. The organization primarily scans and analyzes radio signals from space, captured by powerful telescopes. The idea is that scientists can distinguish a signal that comes from an intelligent source. Though she hasn't found E.T. yet, Tarter isn't discouraged. She'll now work on raising funds to support SETI research.

Jill Tarter has a physics degree from Cornell, and a Ph.D. in astronomy from the University of California-Berkeley. She's won a number of scientific awards, including two NASA public service medals. Her work was an inspiration for the Carl Sagan novel "Contact." The film adaptation starred Jodie Foster, who visited Tarter to prepare for her role.

Tarter spoke with FRESH AIR contributor Dave Davies.

DAVE DAVIES, HOST:

Well, Jill Tarter, welcome to FRESH AIR. When you were studying, when you were an engineer, did you think much about the prospects for extraterrestrial life at all? Were you interested in the subject?

JILL TARTER: Not as an undergraduate. Early in my life, I had spent a lot of time with my father, who had studied astronomy as well as being a professional football player. And we'd walk along the beaches of the west coast of Florida - very dark skies - look up, and beautiful stars. And I assumed, at that time, that along some beach on some planet around one of those stars, there would be a small creature walking with her - or its - dad, and they would see our sun in their sky, and they might wonder whether anyone was there.

DAVIES: So...

TARTER: But I never thought about it professionally until graduate school.

DAVIES: So what got you seriously interested in this subject?

TARTER: Actually, an accident. When I started in graduate school, I learned how to program a PDP-8/S computer. That was the first time that scientists had any real computing power on our desktops. It was wonderful - and it was stupid. I mean, it had no language; you had to program it, noctal(ph), had to set all the ones and zeroes. But it was a marvelous device. Many years later, it was given as a piece of surplus equipment to an X-ray astronomer, Stu Bowyer, who had a great idea about the possibility of piggybacking on the normal radio astronomy observing that was going on at Hat Creek Radio Observatory, that was run by University of California-Berkeley. And so Stu talked to Jack Welch, who is now my husband, about doing a SETI project. And Jack said, sounds cool to him. Stu didn't have any money, so he went begging equipment. One of the pieces of equipment was this PDP-8/S, and somebody told Stu that I used to work on that machine. He came to my office; gave me something called the Cyclops Report, an engineering design study done by NASA-Ames about searching for extraterrestrial intelligence.

I read that engineering study cover to cover. It was phenomenal. I realized that after millennia of people asking the priests, the philosophers - whoever they thought was wise, what we should believe about whether or not we're alone in the universe; could now be superseded by doing an experiment, by doing a scientific exploration using the tools of the astronomers. And here I was, in exactly the right place with the right skill sets, at the right time. And I got hooked.

DAVIES: And this was - what, back in the '70s?

TARTER: It was in the mid-'70s, yes.

DAVIES: When you search for extraterrestrial intelligence, what do you do? It involves radio telescopes, right?

TARTER: Well, the search for extraterrestrial intelligence is actually a misnomer. We don't know how to identify intelligence over interstellar distances. What we do, instead, is use technology as a proxy. And we say, can we look, or listen, in any way that could detect technologies that someone else might be using; and that might be modifying their environment in ways that are detectable over interstellar distances?

And pragmatically, to date, that means we're using radio telescopes to listen for signals that are generated either for their own purposes - and we just eavesdrop on the leakage - or they're beacons, intended to attract the attention of us - an emerging, young technology in the galaxy. And at optical wavelengths, instead of looking for signals that occupy only one, narrow range of frequency - which is what we do in the radio - in the optical, we look for signals that are broadband - flashes of light - that last for a billionth of a second or less. And we're constantly thinking about, what's the next new technology that we might innovate; which in turn, could be a better way of looking for extraterrestrial technologies. We do reserve the right to get smarter, and we certainly don't think that we know all there is to know.

DAVIES: Now, you said in the optical (unintelligible) you're looking for bright flashes that last a billionth of a second. Why?

TARTER: Or less, because that's what a laser can do. Mother Nature does not seem to be able to do that extreme time compression to produce a bright signal in a very short period of time. But lasers can do it, no problem. And if you take lasers, and you focus them with big mirrors, you can get enormously bright signals that for that billionth of a second, outshine the stars.

DAVIES: OK. And radio astronomy, why is there so much radio astronomy? And how does the search for extraterrestrial intelligence use that technology to look for signals of interest?

TARTER: Well, radio astronomy, optical astronomy, X-ray astronomy, gamma ray astronomy - they're all studying light, but light at different wavelengths. So each part of the electromagnetic spectrum allows us to learn something different about the universe, and about its physical properties. So radio wavelengths are just long, tired light. If you're looking for signals that have persistence, that - the radio part of the spectrum; and looking for signals that occupy only one channel on the radio dial; our good guess is for something that's obviously engineered and at the optical end of the spectrum, that - the bright flashes that last only a billionth of a second - not capable in terms of Mother Nature. These are the artifacts we're looking for now. So we are hopeful that if we're looking for the right thing - the radio signals, and the bright optical flashes - that within a few decades, we will have either succeeded, or done a significantly large search of our portion of the galaxy, that any negative results would, in fact, be significant.

DAVIES: Over the years, you - and those of you involved in this - have been looking at radio transmissions. How do you distinguish a radio signal from - I guess what you would call a normal astrophysical object? How would you distinguish that from something that might come from an intelligent source?

TARTER: Well, early on in my SETI days, that's precisely what I did. I went and used radio telescopes. And we looked at the kinds of objects that we knew about; and we looked at what the emission from these objects was like. And it became very clear that nature was incapable of compressing a great deal of emission into only a very narrow range of radio frequencies. Nature tends to create sources of radio emission that fill the channel; that are broadband. And so we studied the narrowest features that we could find in the radio spectrum - those were saturated OH masers. And therefore, we said, well, that's our sandbox. For technical reasons, for reasons of economy, our technology produces very strong signals with a high signal-to-noise ratio, that are very narrow band. We can do it with technology, but nature does not seem to be able to do that - which is the primary reason we started looking for that particular artifact.

DAVIES: And presumably, if you do detect this signal from a distant civilization, or a distant life form, it's a signal that originated a long time ago, right?

TARTER: Within our galaxy, it could have originated as much as 100,000 years ago; and coming across the galaxy would take that long. That's right.

DAVIES: OK.

TARTER: So we don't know that they're still there, but the chances are very good that they are there. We're a young technology, OK? We're 100 years old in a galaxy that's 10 billion years old. Our star is 5 billion years old, and most of the stars in our neighborhood are a billion years older than our sun. We're looking for advanced technologies because anyone less primitive than us isn't detectable. And advanced technology will be older. If they can get old and send such messages, they can probably continue to survive. So actually, that's one of the great things about SETI.

Starting a new train of thought here, but Phil Morrison, one of the co-authors on that 1959 nature paper on SETI, used to call SETI the archaeology of the future. It's archaeology because the speed of light is finite, and it's taken the signal a long time to get here. So if there's information there, we learn about their past. But if we detect a signal - even if there's no information; even if it's just a cosmic dial tone - we learn that it's possible for us to have a future, a long future. That's because we couldn't possibly be successful with SETI unless technologies, on average, survive for a long time so that they can be lined up not only in three-dimensional space, close enough for us to find them; but in the fourth dimension, in time, so that they are transmitting as we are emerging. I think that is one of the most hopeful things about SETI, this archaeology of our future.

DAVIES: So if we were to find a signal - I mean, you might learn more about it with study, but it's not like you're going to get a real-time conversation with that civilization going.

TARTER: I think that interstellar communication is much more like the really fruitful communication we have with the ancient Greeks and Romans and Shakespeare, right? There's an enormous amount of information that's propagated forward in time; and we learn from it by reading it, even though we can't ask Shakespeare what he thinks about the current election.

DAVIES: There must have been some times, as you've reviewed - you know - these radio signals, that you thought you were onto something. You want to tell us one of those?

TARTER: Yeah, I've actually had a couple of those. And they're amazing, adrenaline moments. Early on in France, in Nozay, I stayed awake for three days till we actually proved the signal was a distant airport, rather than something we were interested in, because I thought my French colleague was going to call up Le Monde and tell them we'd found it. And another instance, I was at Green Bank, West Virginia. And we had a second telescope in Woodberry, Georgia, that helped us discriminate against our own technology. Unfortunately, this telescope got hit by lighting, and we had three days to observe without it. And during that time, of course, we got a signal that was really interesting. And we followed it for almost a whole day before we convinced ourselves that indeed, it was not coming from the star we had been tracking; it was a signal coming in the sidelobes of the telescope. A telescope has peripheral vision, just like your eye. And this was the SOHO spacecraft, which was in a small sidelobe of the telescope all day long because SOHO was orbiting the sun, and so was the planet Earth.

DAVIES: When someone looks at you and says, you know, you've been at this for decades, and we haven't found any discernible - clear, discernible signs of extraterrestrial life; what's the argument that you give them, that there's a real possibility that there's something out there?

TARTER: The argument's easy - we've hardly begun to search. The space that we're looking through is nine-dimensional. If you build a numerical model, the amount of searching that we've done in 50 years is equivalent to scooping one, 8-ounce glass out of the Earth's oceans, looking and seeing, did you catch a fish. No? No fish in that glass? Well, I don't think you're going to conclude that there are no fish in the ocean. You just haven't searched very well yet. That's where we are.

DAVIES: But those who say look, what happened on Earth is such a remarkable accident; that - you know - in the primordial mass, there were amino acids, and then there was - these billion years of evolution that made us who we are; that's just not going to be replicated out there. What gives you some reason to believe that it might be?

TARTER: Well, I would argue that we're intimately connected with the cosmos. We are, in fact, made out of stardust. The iron in the hemoglobin molecules in the blood in your right hand, came from a star that blew up 8 billion years ago. The iron in your left hand came from another star. We are the laws of chemistry and physics, as they have played out here on Earth.

And we are now learning that planets are as common as stars. Most stars, it appears now, will have planets. There are all kinds of different planets, and not every one is going to be like ours. Nor, necessarily, does it have to be. We have been studying extremophiles, that live in incredible conditions - a range of conditions, here on Earth. So the habitable real estate out there is getting larger.

DAVIES: When you say extremophiles, you're talking about life forms here on Earth that live in extraordinary conditions, right?

TARTER: I am. I'm talking about life forms.

DAVIES: Such as?

TARTER: We have microbial life that lives in the boiling battery acids of Grand Prismatic Springs, in Yellowstone. We have life that lives two miles beneath the surface of the Earth. There's more biomass under your feet in the surface of the Earth, than there is on the surface and above.

There's life at black smokers, the bottom of the ocean where the crust is splitting apart; huge temperatures and high densities and no sunlight - and a beautiful collection of tube worms and blind shrimp, and all kinds of wonderful life.

DAVIES: And are these life forms that have a different evolutionary origin from ours? Or are we all branches of the same tree here on Earth?

TARTER: We are related to those life forms. We share a common ancestor with those life forms; and evolution has taken them in directions that allows them to exploit these various niches. We think boiling battery acid is really uncomfortable. They're perfectly evolved to make a living there.

DAVIES: As people contemplate the notion of contact with extraterrestrial civilizations, what do you say to those who say, hey, we don't want to let people know we're here? They might come and, you know, wage war on us, enslave us, exploit us for our natural resources.

TARTER: Right. Stephen Hawking has warned that we shouldn't be transmitting because it didn't work out so nice for the natives when Columbus showed up. Well, that horse is already out of the barn. We've been leaking radiation for about 100 years. So there is information about the technology on this planet, that's now 100 light years away from Earth. And there are many thousands of stars in that vicinity.

So the question is, should we deliberately transmit to try and attract attention? I don't think that we should purposefully - for now. We're the youngest kids on the block. We just barely have enough technology to begin to dabble in this exploration. Let the older civilizations do the harder job of transmitting.

TARTER: Well, we are certainly leaking. That tends to have lower power than we would be able to put into a deliberate transmission. So the leakage is harder to find than deliberate transmissions. I think we should listen first, and transmit when we get older. And I don't worry about the consequences. If they can get here, they are technologically far in advance of the 21st century Earth.

They are an old technology. How did they get to be an old technology? Well, one thing - one way might have been that they outgrew the aggressive tendencies that were probably at the base of their becoming intelligent in the first place. When you look at evolutionary biology - at least, on this planet - one explanation for how intelligence arose is the predator-prey situation that ratchets up intelligence.

But after a while, when the kill power becomes so extreme, then in fact, our evolutionary best strategy might be to back away from that. Steven Pinker has a recent book that argues that we are kinder today than we used to be. So I don't think you can get to be an old technology unless you manage to stabilize your population, husband your resources, and get your world in shape.

And if you've done that, then what we offer them is information, is uniqueness. I think they're - if they were to come here, would be interested in exactly what the laws of physics and chemistry did here, as opposed to what it did where they came from.

DAVIES: They'd be here to explore, not conquer.

TARTER: I think so. If they can get here, they probably can take care of all of the needs that they have, on their own. And the only real source that makes it worthwhile to travel, is information. What's different here, than was back there?

DAVIES: You know a lot of people at NASA. I mean, you've - you know, long-standing ties to astronomers and others in the scientific community. How do you think they regard SETI?

TARTER: Well, I don't have to actually think to answer that question because every 10 years, astronomers and astrophysicists do a self-evaluation; a decadal review. And since the very first one back in the '60s, SETI has been something that the astronomers have chosen to say, it shouldn't be a huge project, but it is certainly worthwhile to invest - small amount of funding - because of the huge, potential payoff. This is, essentially, getting the Good Housekeeping seal of approval from the National Academy of Sciences, when you have a decadal review that recommends that your project be pursued.

DAVIES: Your work inspired the Carl Sagan book "Contact," and then the film with Jodie Foster. Do you have a favorite scene?

TARTER: I have - no. I have a least favorite scene.

(LAUGHTER)

TARTER: I have - there is a problem. I left Arecibo a day before a scene was filmed. It turns out, it's a huge innumeracy in the film. Innumeracy is to numbers what illiteracy is to writing, right? And Jodie Foster is - it's just before the first kiss, so she's out on the balcony behind the control room at Arecibo, and they're looking at the stars in the beautiful telescope. And she's doing - oh, look at all those stars. If only one in a million of those stars had planets, and if only one in a million of those planets had life, and if only one in a million of those life forms were transmitting, there would be millions of signals for us to detect.

Well, the math's all wrong. It's really annoying.

(LAUGHTER)

TARTER: There are 10 to the 11- a hundred billion - stars in the Milky Way galaxy. And even if she was looking up and seeing them all - which she wasn't because your eye only sees a few thousand stars, but let's say she's seeing them all. She's multiplying 10 to the 11 by 10 minus 18, and coming up with 10 to the sixth. That's wrong by 13 orders of magnitude.

And the really sad story is that Carl Sagan died while this movie was being edited. There was a memorial service for Carl at JPL - in the spring, after he died in December. And Ann Druyan wanted to show the assembled engineers and scientists a clip from the film. But since it was still being edited, Warner Brothers didn't want to give her a clip that might not end up in the film.

But here, this is just before the first kiss, so this is setting up the romantic piece in the film and they know they're not going to lose this. So this is the clip that Annie shows. And you kind of hear this, ohhhh! gasp, at the end, from all the scientists and engineers, who can - obviously - do the math, and know it's wrong. And we tried to get it changed, but you can't loop it; it's too close up on her face. And that was sad.

DAVIES: OK. So what should the script have read?

TARTER: Well, you'd be much closer if you said one in a thousand. And then you would have been OK.

DAVIES: OK. So the fact that she ends up in this kind of pod and has this amazing contact with this other civilization, and someone appears in the representation of his father - her father; that didn't bother you. But the innumeracy got to you, huh?

TARTER: No. I'm ready to go. If I could have that experience, I'm good to go. Right? Let's do it. I'd go in a heartbeat. But, yeah, you're not going to get there unless you get the math right.

DAVIES: Well, Jill Tarter, thanks so much for speaking with us.

TARTER: Dave, it's been my pleasure. Thanks for having me.

GROSS: Jill Tarter spoke with FRESH AIR contributor Dave Davies. Tarter is the former director of research at the SETI Institute. She retired earlier this year, and is now raising money to support the organization. Transcript provided by NPR, Copyright NPR.